Sampling small older populations:

Methods and challenges of a dementia prevalence study

NZSA2024

Claudia Rivera-Rodriguez, PhD

Dementia

  • Dementia is a term used to describe a group of symptoms affecting memory, thinking and social abilities.

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The need for a prevalence study

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New Zealand changing population

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Feasibility study (2020)

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  • Demonstrated that a prevalence study was feasible in Māori, Chinese, Indian and Pākehā

  • We found that the sampling/doorknocking strategy was reasonable

  • We were able to train up multi-ethnic interviewers

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  • Aim: Establish the true current prevalence of dementia in NZ

  • Populations: Chinese, Indian and Pākehā 65yo+

  • This talk presents the sampling design and lessons learned from the IDEA study (so far)

  • There is separate study for Māori (running at the moment too)

Sampling strategy

  • We do not have a reliable frame of people 65yo+

  • Our Chinese and Indian populations are hard to find:

Aotearoa-NZ geography hierarchy

Frame: Territorial autorities

Auckland + Christchurch Region (Christchurch City +Selwyn District+Waimakariri District )

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Sampling phases

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Sample sizes for each domain

  • We wanted a design that would yield about the same margin of error for all ethnic groups (i.e. domains)

  • We run lots of simulations to identify sensible sample parameters:

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Our design: inclusion probabilities-areas

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  • Commercial/Industrial meshblocks with non-residential dwellings: We replace these with the closest meshblock (based on selection probability) from the same area.

  • Door-knocking is expensive and difficult.

  • Training of interviewers in 4 different languages

  • Consent rates vary across ethnicities: Sampling weights will need adjustment for this.

  • Data processing from questionnaires in four different languages.

How is the recruitment going?

Thank you!